The long term goal of this research is a better understanding of the molecular mechanism and regulatory processes involved in the maintenance of the constant pool of plasma iron that is essential for the synthesis of hemoglobin and other important iron-containing systems. It is hoped that studies of this nature will provide insight into the molecular bases of metabolic disorders such as iron deficiency anemia, one of the most common deficiency disorders in humans, and hemochromatosis, the excess storage of iron. The studies in this proposal should provide insight into the mechanism and regulation of one important aspect of iron metabolism, the mobilization of iron from tissue stores. The initial focus of this research will be to assess the relative importance of two hepatic enzymes in the reductive release of iron from ferritin. Studies with control and iron-deficient rats will also be conducted to determine if an increase in the hepatic activity of these enzymes correlates with the acceleration of iron mobilization from liver stores. Experiments will be performed to determine if the in vivo inhibition of one or both of these enzymes by the administration of tungsten-supplemental diets and riboflavin-deficient diets correlates with a progressive accumulation of iron in liver ferritin. Th redox centers of the enzymes will be chemically modified. A comparison of the activities of the native and modified enzymes should provide a better understanding of the mechanism(s) involved in the enzyme-catalyzed removal of iron from ferritin.